A method for removing phenolic compounds and metal ions from carbon dioxide-based polyols

Abstract

The invention relates to the technical field of polymer purification, and discloses a method for removing phenolic compounds and metal ions from carbon dioxide-based polyols, comprising dynamic adsorption and pressure-swing desorption steps, using a combined modified activated carbon adsorbent to feed in proportion, using low-frequency ultrasound for pre-adsorption, and then heating mechanical stirring to dynamically monitor adsorption equilibrium; after adsorption equilibrium, first use inert gas low-pressure filtration, and then use inert gas medium-pressure rapid filtration. The removal rate of phenolic compounds in the purified carbon dioxide-based polyols of the present invention is as high as 99% or more, and the metal ion concentration is less than 2 ppm, and carbon dioxide-based polyols with extremely high quality can be obtained efficiently and quickly.

Description

Technical Field

[0001] The invention relates to the technical field of polymer purification, and in particular to a method for removing phenolic compounds and metal ions from carbon dioxide-based polyols. Background Art

[0002] Carbon dioxide-based polyols are formed by polymerization of carbon dioxide, propylene oxide and phenolic compound initiators under the action of bimetallic catalysts. The structure of carbon dioxide-based polyols combines the characteristics of polyester and polyether. It not only inherits the excellent mechanical strength and modulus of polyester polyols, but also has the excellent water resistance of polyether. However, despite the excellent performance of this polyol, it is still difficult to completely avoid the problem of residual metal ions and phenolic compounds.

[0003] During the production process, CO2-based polyols exhibit different excellent properties depending on the addition of different initiators. Phenolic compounds (such as bisphenol A) as additives make polymer products have excellent properties in terms of high modulus, acid resistance, and hydrolysis resistance. However, there is also the problem that residual phenolic compounds cannot be removed. This problem is particularly difficult because it directly affects the processing properties of the polymer and the performance of the final product. For example, residual bisphenol A and other phenolic compounds will react with other components in the polymer, resulting in changes in the molecular chain structure, which in turn affects the polymer's melt fluidity, formability, thermal stability and other processing properties. These changes will lead to reduced production efficiency, fluctuations in product quality and increased costs. At the same time, residual phenolic compounds also affect the final product properties of the polymer, such as mechanical properties, heat resistance, and weather resistance, thereby reducing the product's service life and market competitiveness.

[0004] During the synthesis of CO2-based polyols, cobalt-zinc bimetallic catalysts are usually used, and some of these metal ion catalysts will remain. The residual cobalt and zinc metal ions not only affect the color and transparency of the product, but also affect the use and storage. Excessive metal ion residues will cause the CO2-based polyols to decompose during storage and produce volatile by-products. If the metal ions cannot be removed in time, when the CO2-based polyols are used to make the downstream product polyurethane, adverse reactions will occur, producing thermally unstable allophanates, thereby affecting the performance of polyurethane. In addition, a large number of studies have found that the residual metal ions will be affected by temperature during the synthesis process, and some will have a slightly light yellow color. The higher the temperature, the darker the yellow. In the purification of CO2-based polyols, decolorization is also a particularly important aspect.

[0005] Therefore, in view of the above problems, the purification of CO2-based polyols is necessary, especially for industrially produced CO2-based polyols, which must ensure product quality and consider production costs. There are two major factors that determine the quality of purification: one is the performance of the adsorbent, and the other is the design of the adsorption process. Specifically, (1) Different types of adsorbents, such as activated carbon and molecular sieves, have different adsorption characteristics and selectivity. They need to be designed specifically according to the particularity of the adsorption scenario, considering their pore structure, surface chemical properties, and interactions with target products and impurities. In industrial production, it is also necessary to consider the easy filtration and non-clogging and regeneration performance of the adsorbent to increase the number of cycles and life of the adsorbent, improve practicality, and reduce production costs. (2) On the one hand, the matching adsorption process design can make the adsorbent play the best effect and achieve excellent adsorption effect without damaging the purified substance and adsorbent. For example, if the process temperature is set improperly, the adsorbent may be deactivated or destroyed. If the pH of the adsorption environment is not matched, the purified product may decompose. On the other hand, the analytical process is also an important factor in determining the regeneration performance of the adsorbent, which can reduce production costs.

[0006] When CO2-based polyols containing residual metal ions and phenolic compounds are used as the purified substance, the special adsorption environment places more stringent requirements on the adsorbent and adsorption process, which is reflected in the following aspects:

[0007] (1) Difficulty in adsorption due to the characteristics of high molecular weight polymers: CO2-based polyols are high molecular weight polymers with high viscosity, which significantly reduces their fluidity, making it difficult for the adsorbent to fully diffuse in the polymer. The effective contact with the adsorbate (phenolic compounds and metal ions) is limited, thus affecting the adsorption efficiency and uniformity.

[0008] (2) Poor solubility: CO2-based polyols are insoluble in many common solvents, which limits the application of solvent-assisted adsorption methods. Therefore, it is difficult to find a suitable solvent system to optimize the adsorption process, which increases the complexity of the adsorption process.

[0009] (3) When removing phenolic compounds, residual metal ions compete with phenolic compounds for adsorption sites on the adsorbent: In the synthesis of CO2-based polyols, cobalt-zinc bimetallic catalysts are usually used. Some of these metal ion catalysts will remain and interact with the adsorbent, which may occupy adsorption sites or change the charge distribution on the adsorbent surface, thereby reducing its adsorption capacity for phenolic compounds.

[0010] (4) Unstable adsorption environment: Residual metal ions may cause the CO2-based polyols to decompose during storage, producing volatile by-products. This instability increases the complexity of the adsorption process, so it is necessary to ensure that the polymer does not decompose during the adsorption process as much as possible.

[0011] (5) The adsorption and desorption processes have strict requirements: Due to the high viscosity, insolubility, instability and easy decomposition of CO2-based polyols, the adsorption and desorption process parameters (such as pH, temperature, and pressure) are more difficult to design and more difficult to achieve precise control.

[0012] In summary, based on the characteristics of CO2-based polyols, the prior art has not found a method suitable for industrial production that can simultaneously and efficiently remove phenolic compounds and metal ions from CO2-based polyols by adsorption. Summary of the invention

[0013] In view of the problems existing in the prior art, the present invention provides a method for removing phenolic compounds and metal ions in carbon dioxide-based polyols. The dynamic adsorption and pressure-swing desorption methods adopted enable the combined modified activated carbon adsorbent of the present invention to quickly and effectively adsorb phenolic compounds and metal ions in carbon dioxide-based polyols. Low-frequency ultrasonic pre-adsorption can accurately regulate the pore structure of carbon dioxide-based polyols. This regulation helps to optimize the adsorption performance, so that the combined modified activated carbon adsorbent can better meet the adsorption requirements of carbon dioxide-based polyols with higher viscosity. The inert gas pressure-swing desorption process is more conducive to desorbing carbon dioxide-based polyols with higher viscosity from activated carbon, which can improve the desorption efficiency. The pressure-swing desorption helps to desorb substances adsorbed in the deep layer of activated carbon, not just substances on the surface. This deep desorption effect can improve the thoroughness of the overall desorption, improve the yield of purified carbon dioxide-based polyols, and also enable the modified adsorbent to be more fully utilized. The method of the present invention is simple and convenient to operate, can make the removal rate of phenolic compounds in the purified carbon dioxide-based polyols as high as 99% or more, and the metal ion concentration is less than 2 ppm. Carbon dioxide-based polyols with quality that meets downstream production requirements can be obtained efficiently and quickly, with less metal residue, low chroma and high transparency.

[0014] The technical solution of the present invention is as follows:

[0015] The present invention provides a method for removing phenolic compounds and metal ions from carbon dioxide-based polyols, comprising dynamic adsorption and pressure-switching desorption steps, specifically comprising:

[0016] (1) Dynamic adsorption:

[0017] (1-1) adding a combined modified activated carbon adsorbent to a carbon dioxide-based polyol, wherein the combined modified activated carbon adsorbent accounts for 0.09-20 wt% of the mass of the carbon dioxide-based polyol, and pre-adsorbing the combined modified activated carbon adsorbent using low-frequency ultrasound, wherein the combined modified activated carbon adsorbent is nitrogen heterocycle-low-temperature plasma activated-carbon dioxide gas modified;

[0018] (1-2) heating and mechanically stirring to achieve adsorption equilibrium, wherein the adsorption equilibrium refers to dynamic monitoring of the removal rate of phenolic compounds in the carbon dioxide-based polyol to reach more than 99%, and the dynamic monitoring refers to sampling and testing every 30 minutes;

[0019] (2) Transformer solution:

[0020] (2-1) transferring the adsorption equilibrium mixture into a pressurized filter tank, and filtering the mixture with an inert gas at a low pressure to form a filter cake, wherein the low pressure is 0.1-0.7 MPa;

[0021] (2-2) Then, the product is rapidly filtered under medium pressure of an inert gas, wherein the medium pressure is 1-3 MPa, and the filtrate is collected at the bottom of the pressure filter tank to obtain the purified carbon dioxide-based polyol.

[0022] The method for removing phenolic compounds and metal ions from carbon dioxide-based polyols of the present invention comprises the steps of dynamic adsorption and pressure-swing desorption, and the adsorption equilibrium is dynamically monitored by accurately controlling low-frequency ultrasonic pre-adsorption and heating mechanical stirring, and then the parameters of the step of low-medium pressure pressure-swing desorption in an inert gas are coordinated with a combined modified activated carbon adsorbent modified by nitrogen heterocycle-low-temperature plasma activation-carbon dioxide gas, and the above step parameters are related to each other, progressive layer by layer, and play an overall synergistic role, so that the removal rate of phenolic compounds in the purified carbon dioxide-based polyols is as high as 99% or more, and the metal ion concentration is less than 2 ppm, and carbon dioxide-based polyols with extremely high quality can be obtained efficiently and quickly. Specifically, the dynamic adsorption process of the present invention comprises low-frequency ultrasonic pre-adsorption and heating mechanical stirring processes, and the low-frequency ultrasonic wave can form tiny bubbles and generate violent eddies and vortices in the bubbles. This effect can accelerate the transmission and diffusion of substances, so that the carbon dioxide-based polyols in the adsorption process can reach the adsorbent surface faster, thereby increasing the adsorption rate and adsorption amount; and ultrasound can also cause vibration and rotation of the carbon dioxide-based polyols, thereby enhancing the contact frequency and time between substances in the adsorption process. This enhancement helps to improve the adsorption efficiency. The pre-adsorption process can accelerate the diffusion rate of the combined modified activated carbon adsorbent in the carbon dioxide-based polyols, avoid the excessive viscosity of the carbon dioxide-based polyols causing the activated carbon to agglomerate therein and be unfavorable for its function, and can also promote its mass transfer process in the pores of the combined modified activated carbon adsorbent, so that the metal ions and phenolic compounds in the carbon dioxide-based polyols have more opportunities to be adsorbed by the activated carbon. The heating and mechanical stirring process can increase the temperature of the carbon dioxide-based polyols, thereby enhancing the movement speed and activity of the carbon dioxide-based polyol molecules, which is more conducive to their rapid adsorption by the combined modified activated carbon adsorbent; the heating and stirring process can also trigger the hydrogen bond and π-π bond interaction between the phenolic compounds in the carbon dioxide-based polyols and the nitrogen heterocyclic activated carbon, making chemical adsorption more likely to occur, which helps to enhance the adsorption effect and stabilize the adsorption of carbon dioxide-based polyols; at the same time, dynamic adsorption monitoring is carried out, and when the adsorption equilibrium is reached, the mixture is transferred in time for pressure swing desorption, which can greatly improve the adsorption efficiency and ensure the thoroughness of the adsorption.

[0023] In the inert gas pressure-swing desorption process, since the present invention is aimed at purifying carbon dioxide-based polyols with relatively high viscosity, an inert gas nitrogen / argon is used as a carrier gas, which is safe in process production. In addition, the inert gas will not introduce new pollutants or cause corrosion to the environment and equipment during the desorption process, nor will it cause the carbon dioxide-based polyols to continue to react. The filter cake after desorption can be washed by a solvent to form a complete desorption and regeneration process flow, further improving the desorption efficiency and economic benefits.

[0024] In one embodiment of the present invention, the combined modified activated carbon adsorbent is selected from any one or more of pyridine modified activated carbon, pyrrole modified activated carbon, pyrimidine modified activated carbon, benzimidazole modified activated carbon, and quinoline modified activated carbon; the specific surface area of ​​the combined modified activated carbon adsorbent is 3000-5000 m 2 / g, average volume particle size 10-40 μm.

[0025] In one embodiment of the present invention, the combined modified activated carbon adsorbent is prepared through the steps of pre-dispersion and combined modification, specifically comprising:

[0026] (1) Pre-dispersion: Dispersing activated carbon in deionized water to prepare an activated carbon dispersion to form an active and stable activated carbon precursor;

[0027] (2) Combined modification: The combined modification includes nitrogen heterocycle-low temperature plasma activation-carbon dioxide gas modification in sequence;

[0028] The nitrogen heterocycle modification method comprises adding the nitrogen heterocycle modifier to the activated carbon dispersion at a mass ratio of the nitrogen heterocycle modifier to the activated carbon of 1:0.5-20, and heating and refluxing to prepare the nitrogen heterocycle modified activated carbon;

[0029] The low-temperature plasma activation method comprises subjecting the nitrogen heterocyclic modified activated carbon to low-temperature plasma surface treatment to obtain an activated adsorbent; the low-temperature plasma activation time is 10-60 min; when the activation time is less than 10 min, the specific surface area will be less than 3000 m 2 / g, the average volume particle size is higher than 40 μm, and when the activation time is higher than 60 min, the specific surface area will decrease with time; the gas required for the low-temperature plasma activation is nitrogen, and the gas environment can promote the increase of nitrogen-containing functional groups on the surface of the activated carbon, while if other environmental gases are used, it will lead to the increase of its oxygen-containing acidic functional groups, which is not conducive to the adsorption of phenolic compounds; the low temperature of the low-temperature plasma refers to the temperature range of 30°C-100°C; low-temperature plasma treatment can keep the activated carbon between 10-40 μm, and the activated carbon within this range can not only ensure the good dispersibility of the activated carbon particles in the carbon dioxide-based polyols, but also form an effective filter cake, while avoiding the problems of product mixing and filtration difficulties, and the activated carbon is not prone to clogging problems. With the appropriate filtering means, the purified product can be obtained quickly and efficiently.

[0030] The method for modifying the carbon dioxide gas is to prepare a solution of the activated adsorbent using water as a solvent, disperse and immerse it, and purge it with low-pressure carbon dioxide gas at a pressure of 0.2-1.5 MPa until the solution pH is 6-8, filter it, and vacuum dry it to obtain the combined modified activated carbon adsorbent.

[0031] In one embodiment of the present invention, in step (1-1), the low-frequency ultrasonic wave has a frequency of 10-40 kHz;

[0032] In one embodiment of the present invention, the pre-adsorption temperature is 30-70 °C;

[0033] In one embodiment of the present invention, the pre-adsorption time is 1-5 h;

[0034] In one embodiment of the present invention, the combined modified activated carbon adsorbent accounts for 0.1-10 wt % of the mass of the carbon dioxide-based polyol.

[0035] In one embodiment of the present invention, in step (1-2), the heating temperature is 30-90° C., the mechanical stirring time is 4-10 h, and the stirring rate is 800 r / min-1600 r / min.

[0036] In one embodiment of the present invention, the detection and calculation method of the removal rate of the phenolic compounds is as follows: using an ultraviolet spectrophotometer to detect the absorbance corresponding to the maximum absorption wavelength (Amax) of the phenolic compounds, and then calculating a standard curve according to the Lambert-Beer law, and finally obtaining the concentration of the phenolic compounds in the carbon dioxide-based polyol, and then calculating the removal rate of the phenolic compounds according to the following formula;

[0037]

[0038] ŋ represents the removal rate of phenolic compounds (%), C0 represents the initial concentration of phenolic compounds in CO2-based polyols (mg / L), C t It represents the concentration of phenolic compounds in CO2-based polyols after adsorption by the modified adsorbent (mg / L).

[0039] In one embodiment of the present invention, the low pressure filtration time is 0.5-2 h and the temperature is 25±5°C;

[0040] In one embodiment of the present invention, the medium-pressure rapid filtration time is 1-8 h, and the temperature is 20-90°C; more preferably, the medium-pressure rapid filtration time is 1-4 h, and the temperature is 20-50°C.

[0041] The variable pressure desorption process of the present invention adopts a method of combining low pressure to form a filter cake and then medium pressure rapid filtration. Under low pressure conditions, the carbon dioxide-based polyol adsorbed on the activated carbon can be initially desorbed by adjusting the low pressure to form a desorption filter cake, which is helpful for the initial separation of the carbon dioxide-based polyol and lays the foundation for subsequent medium pressure rapid filtration. Subsequently, rapid filtration under medium pressure conditions can further improve the separation efficiency of the desorption product, and the medium pressure can enhance its fluidity, so that the desorption product passes through the filter cake faster, thereby achieving efficient separation; the desorption filter cake formed by low pressure reduces the re-adsorption opportunity of the carbon dioxide-based polyol on the combined modified activated carbon adsorbent to a certain extent, and the medium pressure rapid filtration can more thoroughly remove the phenolic compounds and metal ions in the desorption product, thereby improving the purity of the desorption product; appropriate heating during medium pressure rapid filtration can enhance the thermal motion speed of the carbon dioxide-based polyol, reduce its adsorption performance, and thus more easily desorb from the surface of the combined modified activated carbon adsorbent. Heating can also cause certain changes in the microporous structure of the combined modified activated carbon adsorbent, which is helpful for the release of carbon dioxide-based polyols; the combination of low-pressure preliminary desorption and medium-pressure rapid filtration in the present invention shortens the time period of overall desorption and separation, thereby accelerating the regeneration speed of the combined modified activated carbon adsorbent, and the rapid and efficient desorption and filtration process improves the regeneration efficiency of the combined modified activated carbon adsorbent, thereby increasing the production capacity of the entire treatment system.

[0042] In one embodiment of the present invention, the carbon dioxide-based polyol is prepared by polymerization of carbon dioxide, propylene oxide and phenol initiator under the action of cobalt-zinc double metal cyanide catalyst, and has a viscosity greater than 7000 mPa·s at 70° C. Preferably, the carbon dioxide-based polyol has a number average molecular weight of 1000-15000 and a molecular weight distribution of less than 2.

[0043] In one embodiment of the present invention, the contents of metal cobalt and zinc in the purified carbon dioxide-based polyol are both lower than 2 ppm, and the removal rate of phenolic compounds is above 99%.

[0044] In one embodiment of the present invention, in step (2-2), the filter cake collected during the medium-pressure rapid filtration is washed with an organic solvent to obtain a regenerated combined modified activated carbon adsorbent;

[0045] In one embodiment of the present invention, the organic solvent is selected from any one or more of ethyl acetate, ethanol, dichloromethane, methanol, and acetonitrile, more preferably dichloromethane;

[0046] In one embodiment of the present invention, the mass ratio of the filter cake to the organic solvent is 1:10-1:400.

[0047] In one embodiment of the present invention, the regenerated combined modified activated carbon adsorbent can be recycled and reused more than three times.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] The present invention provides a method for removing phenolic compounds and metal ions from carbon dioxide-based polyols, which adopts a dynamic adsorption and pressure-swing desorption mode, accurately controls low-frequency ultrasonic pre-adsorption, and dynamically monitors adsorption equilibrium by heating mechanical stirring, and then passes through the combined modified activated carbon adsorbent of the present invention through the step parameters of low-medium pressure pressure-swing desorption in an inert gas, and the above step parameters are linked before and after, progressively layer by layer, and play an overall synergistic role, so that the combined modified activated carbon adsorbent can quickly and effectively adsorb phenolic compounds and metal ions in carbon dioxide-based polyols, and the low-frequency ultrasonic pre-adsorption can accurately regulate the carbon dioxide-based polyols. The pore structure of the present invention is conducive to optimizing the adsorption performance, so that the combined modified activated carbon adsorbent can better adapt to the adsorption requirements of the carbon dioxide-based polyols with large viscosity; and the inert gas pressure-swing desorption process is more conducive to desorbing the carbon dioxide-based polyols with large viscosity from the combined modified activated carbon adsorbent, which can improve the desorption efficiency, and the pressure-swing desorption helps to desorb the substances adsorbed in the deep layer of the combined modified activated carbon adsorbent, not only limited to the surface substances, and this deep desorption effect can improve the thoroughness of the overall desorption, improve the yield of the purified carbon dioxide-based polyols, and also make the modified adsorbent more fully utilized. The method of the present invention is simple and convenient to operate, and can make the removal rate of phenolic compounds in the purified carbon dioxide-based polyols as high as 99% or more, and the metal ion concentration is less than 2 ppm. The carbon dioxide-based polyols with quality that meets the downstream production requirements can be obtained efficiently and quickly, with less metal residue, low chroma and high transparency. Moreover, the adsorbent used in the present invention can be regenerated and recycled, and the adsorption effect of the recycled use still maintains a high level, improving economic benefits. DETAILED DESCRIPTION

[0050] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only intended to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0051] The detection method of the present invention is as follows:

[0052] The test method of the specific surface area of ​​the present invention is: using the Quantachrome automatic gas adsorption system (AUTOSORB-1-C) of the full adsorption instrument for detection, and using the BET technology N2 adsorption curve to calculate the specific surface area. Before the test, the adsorbent is treated at 200°C under vacuum for 1 hour to prevent dust or water adsorbed in the pores from affecting the test results.

[0053] Average volume particle size test method: The average volume particle size is measured by Nicomp 380 ZLS equipment produced by PSS Company of the United States. Before the measurement, the solid powder is dispersed with deionized water and the suspension is broken up with ultrasound.

[0054] Determination of heavy metal ion Zn and Co content in CO2-based polyols before and after adsorption: Accurately weigh about 1 g of the test substance (accurate to 0.0001 g) and accurately record the weight M 二氧化碳基多元醇 , place the object to be tested in a 100 mL crucible, seal it and preheat it in an electric heating jacket to convert the liquid into a solid. The purpose of sealing is to prevent Zn and Co from being brought into the air with the gas or smoke produced by combustion, causing errors. Usually, a lid is used. Then, place the crucible containing the object to be tested in a muffle furnace, set the temperature to 500°C, heat it for 2 h, and keep it at a constant temperature for 2 h, so that the sample is completely ashed, while Zn and Co remain on the lid and wall of the crucible. Then, use 7% hydrochloric acid solution to dissolve the Zn and Co remaining in the crucible, and prepare a solution in a 100 mL volumetric flask for testing.

[0055] Determination of Zn and Co content in the solution in the volumetric flask by ICP i ,ICP , in ppm, calculate the Zn and Co contents in the sample to be tested according to formula (1);

[0056] C i =(C i ,ICP ×100) / M 二氧化碳基多元醇 (1)

[0057] In the formula, C i Refers to the Zn or Co content in the purified CO2-based polyol sample, ppm;

[0058] C i ,ICP Refers to the Zn or Co content in the test solution measured by ICP, ppm; wherein, the Co content in the test solution before adsorption is 257 ppm, and the Zn content in the test solution before adsorption is 264 ppm;

[0059] M 二氧化碳基多元醇 Refers to the mass of the sample, g.

[0060] Removal rate of phenolic compounds: The absorbance corresponding to the maximum absorption wavelength (Amax) of phenolic compounds was detected by ultraviolet spectrophotometer, and then the standard curve was calculated according to the Lambert-Beer law, and finally the concentration of phenolic compounds in carbon dioxide-based polyols was obtained.

[0061]

[0062] ŋ represents the adsorption rate of modified activated carbon for phenolic compounds (%), C0 represents the initial concentration of phenolic compounds in carbon dioxide-based polyols (mg / L), C t It represents the concentration of phenolic compounds in CO2-based polyols after adsorption by modified activated carbon (mg / L).

[0063] Chroma test

[0064] Take 5 g of the object to be tested and place it in a cuvette. Place the cuvette in a dark environment to reduce the influence of the light source on the test and cause errors. Use an NR10QC colorimeter for testing. The test data includes three basic coordinates L*, a*, and b*.

[0065] The coordinate L* represents the color brightness, L*=0 indicates black, and L*=100 indicates white.

[0066] The coordinate a* represents the position between red / magenta and green, with a negative a* value indicating green and a positive a* value indicating magenta.

[0067] The coordinate b* represents the position between yellow and blue, a negative b* value indicates blue, and a positive b* value indicates yellow.

[0068] When a* and b* approach 0, the sample is closer to colorless.

[0069] In the present invention, when the L value approaches 100, it indicates that the product has a higher whiteness quality, that is, the brightness is better; and the closer the a* and b* values ​​are to 0, it means that the product exhibits higher transparency and better color purity, that is, the chromaticity performance is better.

[0070] The untreated carbon dioxide-based polyol used in the following specific embodiments has a chromaticity test result of L*=48.88, a*=0.75, and b*=2.53.

[0071] Example 1

[0072] Preparation of combined modified activated carbon adsorbent: The combined modified activated carbon adsorbent is prepared through the steps of pre-dispersion and combined modification, specifically comprising:

[0073] (1) Pre-dispersion: Dispersing activated carbon in deionized water to prepare an activated carbon dispersion to form an active and stable activated carbon precursor;

[0074] (2) Combined modification: The combined modification includes nitrogen heterocycle-low temperature plasma activation-carbon dioxide gas modification in sequence;

[0075] (2-1) nitrogen heterocycle modification: adding the nitrogen heterocycle modifier to the activated carbon dispersion at a mass ratio of 1:0.5-20, and heating under reflux to prepare nitrogen heterocycle modified activated carbon;

[0076] (2-2) The method of low-temperature plasma activation is to subject the nitrogen heterocyclic modified activated carbon to low-temperature plasma surface treatment to obtain an activated adsorbent;

[0077] (2-3) Carbon dioxide gas modification: The activated adsorbent is prepared into a solution using water as a solvent, dispersed and soaked, and purged with carbon dioxide gas until the solution pH is 6-8, filtered, and vacuum dried to obtain the combined modified activated carbon adsorbent. The preparation parameters of multiple combined modified activated carbon adsorbents are shown in Table 1.

[0078] Table 1 Preparation parameters of modified adsorbent

[0079]

[0080] The combined modified activated carbon adsorbents X-1, X-2, X-3, and X-4 prepared in Example 1 were used for the purification of carbon dioxide-based polyols, which are respectively recorded as Examples 2-5, as follows:

[0081] Example 2

[0082] (1) Dynamic adsorption:

[0083] (1-1) 20 g of the combined modified activated carbon adsorbent (X-1) was placed in a container containing 100 g of carbon dioxide-based polyol and subjected to ultrasonic oscillation treatment using 40 kHz low-frequency ultrasound. The ultrasonic time was 1 h and the ultrasonic temperature was set to 70 °C.

[0084] (1-2) The mixture after ultrasonic treatment in step (1-1) was stirred by mechanical stirring at a temperature of 90°C to ensure uniform stirring. The adsorbent and the carbon dioxide-based polyol were well integrated for adsorption experiments. Sampling was performed every 30 minutes. The results of the 4-hour test showed that the adsorption reached equilibrium and the removal rate of phenolic compounds reached 99.5%.

[0085] (2) Transformer solution:

[0086] (2-1) transferring the adsorption equilibrium mixture into a pressurized filter tank, filtering the mixture with an inert gas at low pressure to form a filter cake, wherein the pressure is 0.1 MPa, and after 2 hours at 30° C., a dense filter cake is formed by observing through the filter tank observation port;

[0087] (2-2) Then, the product was filtered quickly under medium pressure of inert gas, wherein the medium pressure was 1 MPa and the filtration temperature was 90°C. After 1 hour, the product was completely filtered out, and the filtrate was collected at the bottom of the pressure filter tank to obtain the purified carbon dioxide-based polyol. The performance parameters of the purified carbon dioxide-based polyol are shown in Table 2.

[0088] Example 3

[0089] (1) Dynamic adsorption:

[0090] (1-1) 5 g of the combined modified activated carbon adsorbent (X-2) was placed in a container containing 500 g of carbon dioxide-based polyol and subjected to ultrasonic oscillation treatment using 20 kHz low-frequency ultrasound. The ultrasonic time was 5 h and the ultrasonic temperature was set to 30 °C.

[0091] (1-2) The mixture after ultrasonic treatment in step (1-1) was stirred by mechanical stirring at a temperature of 30°C to ensure uniform stirring. The adsorbent and the carbon dioxide-based polyol were well integrated for adsorption experiments. Sampling was performed every 30 minutes. The results of the 10-hour test showed that the adsorption reached equilibrium and the removal rate of phenolic compounds reached 99.3%.

[0092] (2) Transformer solution:

[0093] (2-1) transferring the adsorption equilibrium mixture into a pressurized filter tank, filtering the mixture under low pressure with an inert gas to form a filter cake, wherein the pressure is 0.7 MPa, and after 0.5 h at 25° C., a dense filter cake is formed by observing through an observation port of the filter tank;

[0094] (2-2) Then, the product was filtered quickly under medium pressure of inert gas, wherein the medium pressure was 3 MPa and the filtration temperature was 20°C. After 8 hours, the product was completely filtered out, and the filtrate was collected at the bottom of the pressure filter tank to obtain the purified carbon dioxide-based polyol. The performance parameters of the purified carbon dioxide-based polyol are shown in Table 2.

[0095] Example 4

[0096] (1) Dynamic adsorption:

[0097] (1-1) 0.09 g of the combined modified activated carbon adsorbent (X-3) was placed in a container containing 100 g of carbon dioxide-based polyol and subjected to ultrasonic oscillation treatment using 30 kHz low-frequency ultrasound. The ultrasonic time was 3 h and the ultrasonic temperature was set to 50 °C.

[0098] (1-2) The mixture after ultrasonic treatment in step (1-1) was stirred by mechanical stirring at a temperature of 60°C to ensure uniform stirring. The adsorbent and the carbon dioxide-based polyol were well integrated for adsorption experiments. Sampling was performed every 30 minutes. The results of the 7-hour test showed that the adsorption reached equilibrium and the removal rate of phenolic compounds reached 99.8%.

[0099] (2) Transformer solution:

[0100] (2-1) transferring the adsorption equilibrium mixture into a pressurized filter tank, filtering the mixture with an inert gas at low pressure to form a filter cake, wherein the pressure is 0.5 MPa, and after 1.5 hours at 28° C., a dense filter cake is formed by observing through the filter tank observation port;

[0101] (2-2) Then, the product was filtered quickly under medium pressure of inert gas, wherein the medium pressure was 2 MPa and the filtration temperature was 60°C. After 3 hours, the product was completely filtered out, and the filtrate was collected at the bottom of the pressurized filter tank to obtain the purified carbon dioxide-based polyol. The performance parameters of the purified carbon dioxide-based polyol are shown in Table 2.

[0102] Example 5

[0103] (1) Dynamic adsorption:

[0104] (1-1) 5 g of the combined modified activated carbon adsorbent (X-4) was placed in a container containing 500 g of carbon dioxide-based polyol and subjected to ultrasonic oscillation treatment using 25 kHz low-frequency ultrasound. The ultrasonic time was 4 h and the ultrasonic temperature was set to 40 °C.

[0105] (1-2) The mixture after ultrasonic treatment in step (1-1) was stirred by mechanical stirring at a temperature of 40°C to ensure uniform stirring. The adsorbent and the carbon dioxide-based polyol were well integrated for adsorption experiments. Sampling was performed every 30 minutes. The results of the 7-hour test showed that the adsorption reached equilibrium and the removal rate of phenolic compounds reached 99.5%.

[0106] (2) Transformer solution:

[0107] (2-1) transferring the adsorption equilibrium mixture into a pressurized filter tank, filtering the mixture with an inert gas at low pressure to form a filter cake, wherein the pressure is 0.4 MPa, and after 1.5 hours at 26° C., a dense filter cake is formed through the observation port of the filter tank;

[0108] (2-2) Then, the product was filtered quickly under medium pressure of inert gas, wherein the medium pressure was 2.5 MPa and the filtration temperature was 80°C. After 4 hours, the product was completely filtered out, and the filtrate was collected at the bottom of the pressure filter tank to obtain the purified carbon dioxide-based polyol. The performance parameters of the purified carbon dioxide-based polyol are shown in Table 2.

[0109] Comparative Example 1

[0110] Referring to the preparation method of Example 2, the only difference is that low-frequency ultrasound is not used for pre-adsorption, and the purification steps are as follows:

[0111] (1) Dynamic adsorption:

[0112] 20 g of combined modified activated carbon adsorbent (X-1) was put into a container of 100 g of carbon dioxide-based polyol and stirred by mechanical stirring at a temperature of 90 °C to make it evenly stirred. The adsorbent and carbon dioxide-based polyol were well integrated for adsorption experiments. Sampling was performed every 30 min. The 4-hour test results showed that the removal rate of phenolic compounds reached 57.6%.

[0113] (2) Transformer solution:

[0114] (2-1) transferring the adsorption equilibrium mixture into a pressurized filter tank, filtering the mixture with an inert gas at low pressure to form a filter cake, wherein the pressure is 0.1 MPa, and after 2 hours at 30° C., a dense filter cake is formed by observing through the filter tank observation port;

[0115] (2-2) Then, the product was filtered quickly under medium pressure of inert gas, wherein the medium pressure was 1 MPa and the filtration temperature was 90°C. After 1 hour, the product was completely filtered out, and the filtrate was collected at the bottom of the pressure filter tank to obtain the purified carbon dioxide-based polyol. The performance parameters of the purified carbon dioxide-based polyol are shown in Table 2.

[0116] Comparative Example 2

[0117] Referring to the preparation method of Example 2, the only difference is that the combined modified activated carbon adsorbent described in the present invention is not used, but commercial coconut shell activated carbon is used as the adsorbent, and the purification steps are as follows:

[0118] (1) Dynamic adsorption:

[0119] (1-1) 20 g of coconut shell activated carbon adsorbent was placed in a container containing 100 g of carbon dioxide-based polyol and subjected to ultrasonic oscillation treatment using 40 kHz low-frequency ultrasound. The ultrasonic time was 1 h and the ultrasonic temperature was set to 70 °C.

[0120] (1-2) The mixture after ultrasonic treatment in step (1-1) was stirred by mechanical stirring at a temperature of 90°C to ensure uniform stirring. The adsorbent and the carbon dioxide-based polyol were well integrated for adsorption experiments. Sampling was performed every 30 minutes. The 4-hour test results showed that the removal rate of phenolic compounds reached 12.7%.

[0121] (2) Transformer solution:

[0122] (2-1) transferring the adsorption equilibrium mixture into a pressurized filter tank, filtering the mixture with an inert gas at low pressure to form a filter cake, wherein the pressure is 0.1 MPa, and after 2 hours at 30° C., a dense filter cake is formed by observing through the filter tank observation port;

[0123] (2-2) Then, the product was filtered quickly under medium pressure of inert gas, wherein the medium pressure was 1 MPa and the filtration temperature was 90°C. After 1 hour, the product was completely filtered out, and the filtrate was collected at the bottom of the pressure filter tank to obtain the purified carbon dioxide-based polyol. The performance parameters of the purified carbon dioxide-based polyol are shown in Table 2.

[0124] Comparative Example 3

[0125] Referring to the preparation method of Example 2, the only difference is that the pressure-switching desorption is not used, and the medium-pressure desorption is uniformly used. The purification steps are as follows:

[0126] (1) Dynamic adsorption:

[0127] (1-1) 20 g of the combined modified activated carbon adsorbent (X-1) was placed in a container containing 100 g of carbon dioxide-based polyol and subjected to ultrasonic oscillation treatment using 40 kHz low-frequency ultrasound. The ultrasonic time was 1 h and the ultrasonic temperature was set to 70 °C.

[0128] (1-2) The mixture after ultrasonic treatment in step (1-1) was stirred by mechanical stirring at a temperature of 90°C to ensure uniform stirring. The adsorbent and the carbon dioxide-based polyol were well integrated for adsorption experiments. Sampling was performed every 30 minutes. The results of the 4-hour test showed that the adsorption reached equilibrium and the removal rate of phenolic compounds reached 99.5%.

[0129] (2) Medium pressure solution:

[0130] The product was completely filtered out after 1 h by using an inert gas medium pressure rapid filtration, the medium pressure being 1 MPa and the filtration temperature being 90°C. The filtrate was collected at the bottom of the pressurized filtration tank to obtain purified carbon dioxide-based polyols. The performance parameters of the purified carbon dioxide-based polyols are shown in Table 2.

[0131] Comparative Example 4

[0132] Referring to the preparation method of Example 2, the only difference is that the ratio of the adsorbent to the carbon dioxide-based polyol used is 30 wt %, and the purification steps are as follows:

[0133] (1) Dynamic adsorption:

[0134] (1-1) 30 g of the combined modified activated carbon adsorbent (X-1) was placed in a container containing 100 g of carbon dioxide-based polyol and subjected to ultrasonic oscillation treatment using 40 kHz low-frequency ultrasound. The ultrasonic time was 1 h and the ultrasonic temperature was set to 70 °C.

[0135] (1-2) The mixture after ultrasonic treatment in step (1-1) was stirred by mechanical stirring at a temperature of 90°C to ensure uniform stirring. The adsorbent and the carbon dioxide-based polyol were well integrated for adsorption experiments. Sampling was performed every 30 minutes. The results of the 4-hour test showed that the adsorption reached equilibrium and the removal rate of phenolic compounds reached 71.9%.

[0136] (2) Transformer solution:

[0137] (2-1) transferring the adsorption equilibrium mixture into a pressurized filter tank, filtering the mixture with an inert gas at low pressure to form a filter cake, wherein the pressure is 0.1 MPa, and after 2 hours at 30° C., a dense filter cake is formed by observing through the filter tank observation port;

[0138] (2-2) Then, the product was filtered quickly under medium pressure of inert gas, wherein the medium pressure was 1 MPa and the filtration temperature was 90°C. After 1 hour, the product was completely filtered out, and the filtrate was collected at the bottom of the pressure filter tank to obtain the purified carbon dioxide-based polyol. The performance parameters of the purified carbon dioxide-based polyol are shown in Table 2.

[0139] Comparative Example 5

[0140] Referring to the preparation method of Example 2, the only difference is that heating mechanical stirring and adsorption monitoring are not used, and the purification steps are as follows:

[0141] (1) Dynamic adsorption:

[0142] (1-1) 20 g of the combined modified activated carbon adsorbent (X-1) was placed in a container containing 100 g of carbon dioxide-based polyol and subjected to ultrasonic oscillation treatment using 40 kHz low-frequency ultrasound. The ultrasonic time was 1 h and the ultrasonic temperature was set to 70 °C.

[0143] (2) Transformer solution:

[0144] (2-1) transferring the adsorption equilibrium mixture into a pressurized filter tank, filtering the mixture with an inert gas at low pressure to form a filter cake, wherein the pressure is 0.1 MPa, and after 2 hours at 30° C., a dense filter cake is formed by observing through the filter tank observation port;

[0145] (2-2) Then, the product was filtered quickly under medium pressure of inert gas, wherein the medium pressure was 1 MPa and the filtration temperature was 90°C. After 1 hour, the product was completely filtered out, and the filtrate was collected at the bottom of the pressure filter tank to obtain the purified carbon dioxide-based polyol. The performance parameters of the purified carbon dioxide-based polyol are shown in Table 2.

[0146] Table 2 Purification conditions and product performance test table of examples and comparative examples

[0147]

[0148] As can be seen from Table 2, the method of the embodiment of the present invention has excellent purification effect. Within the scope of the present invention, the type of modified adsorbent, the amount of modified adsorbent, the low-frequency ultrasonic frequency, the desorption pressure and other parameters can achieve excellent purification effect. The Zn ion content and the Co ion content in the purified product are both less than 2 ppm, and the removal rate of phenolic compounds reaches more than 99%. In terms of chromaticity, the L* value of the embodiment of the present invention is higher than that of the comparative example, and the a* and b* values ​​are lower than those of the comparative example. This shows that the purified product of the comparative example is darker and yellower in color, and the carbon dioxide-based polyol purified by the embodiment of the present invention is whiter and more transparent, and has higher quality. In Comparative Example 1, low-frequency ultrasound was not used for pre-adsorption, resulting in the adsorption process relying only on natural diffusion and traditional heating and stirring methods. The diffusion rate of the adsorbent on the surface of the carbon dioxide-based polyol will be relatively slow, resulting in a low adsorption rate; ultrasonic treatment can not only accelerate the mass transfer process between the surface of the carbon dioxide-based polyol and the adsorbent through physical vibration and cavitation effect, but also improve the microstructure and porosity of the surface of the carbon dioxide-based polyol, making it easier for the adsorbent to enter the interior of the polymer, thereby improving the adsorption efficiency and adsorption amount;

[0149] In Comparative Example 5, mechanical heating and stirring were not used. Heating and stirring are helpful to achieve uniform mixing of materials during the heating process to prevent local overheating or overcooling. If this method is not used and only ultrasonic treatment is relied upon, the temperature and concentration distribution of different components in the mixture will be uneven, thereby affecting the quality and performance of product purification. Mechanical heating and stirring can accelerate the mixing of materials through physical shearing and stirring, while ultrasonic treatment alone can produce cavitation effect and microjets, but its mixing efficiency will be reduced, especially for high-viscosity materials such as carbon dioxide-based polyols. Therefore, the combination of low-frequency ultrasonic treatment and heating mechanical stirring is an indispensable step in the technical solution of the present invention.

[0150] The combined modified activated carbon adsorbent used in the embodiment of the present invention adopts activated carbon as raw material and is prepared through the steps of pre-dispersion and combined modification. The combined modification sequentially includes nitrogen heterocycle-low temperature plasma activation-carbon dioxide gas modification. Compared with the commercial coconut shell activated carbon in Comparative Example 2, on the one hand, the nitrogen heterocycle functional group in the nitrogen heterocycle modifier can form hydrogen bonds with the hydroxyl group in the phenolic compound, which plays a key chemical adsorption effect on the phenolic compound; on the other hand, the alkaline surface generated by the lone pair of electrons of the nitrogen heterocycle forms a competitive relationship with the metal ions, which will reduce the adsorption effect of the adsorbent on the metal ions to a certain extent. At the same time, alkalinity will also affect the stability of the carbon dioxide-based polyol structure. Therefore, in order to avoid the negative impact of nitrogen heterocyclic modification, the present invention further adopts carbon dioxide gas purging modification after nitrogen-containing heterocyclic modification and low-temperature plasma activation. On the one hand, the alkalinity is neutralized to make the environment of the entire modified activated carbon close to neutral, thereby avoiding the decomposition of the carbon dioxide-based polyol by the alkaline adsorbent; on the other hand, the carbon dioxide gas purging modification can generate weak acidic substances with the lone pair electrons of the nitrogen heterocyclic modification, thereby improving the adsorption capacity of metal ions; at the same time, the generated weak acidic substances can also help adjust the pH value of the carbon dioxide-based polyol to make it more stable.

[0151] In Comparative Example 4, more adsorbent was added, but this does not mean that the more adsorbent, the better the adsorption effect. When the amount of adsorbent added is too much, we can clearly observe the problem of adsorbent particle accumulation during the experiment. The improvement of this phenomenon by low-frequency ultrasonic vibration and stirring is not obvious, which will lead to a decrease in the porosity inside the CO2-based polyol, hinder the diffusion of the adsorbent into the CO2-based polyol, thereby reducing the adsorption efficiency. In terms of adsorption capacity, as the amount of adsorbent added increases, although the total adsorption amount may increase, the adsorption capacity per unit mass decreases, which leads to the accumulation between the adsorbent particles, reducing the effective adsorption surface area, so that the adsorbent that can be adsorbed per unit mass of adsorbent is reduced; excessive adsorbent increases its diffusion resistance in the CO2-based polyol, making the adsorption process more difficult; therefore, in our production experiment, 0.09-20 wt% is a reasonable adsorbent addition amount, which can achieve the best adsorption effect and economic benefits. At the same time, low-temperature plasma treatment in the preparation process of combined modified activated carbon adsorbent can keep the activated carbon between 10-40 μm. Activated carbon within this range can not only ensure the good dispersibility of activated carbon particles in CO2-based polyols, but also form an effective filter cake, while avoiding product mixing and filtration difficulties.

[0152] The main difference between Comparative Example 3 and Example 2 is in the desorption process. In Comparative Example 3, the desorption process does not adopt the variable pressure desorption process, but directly adopts the medium pressure desorption process. The omission of the low pressure stage means that the filter cake is not fully formed. The medium pressure directly acts on the material, which will cause the filter cake structure to be loose and uneven, affecting the subsequent filtration effect and the degree of product purification, resulting in its chromaticity and high cobalt and zinc metal content; the material that has not been pretreated at low pressure is directly filtered under medium pressure, and a large filtration resistance is formed due to insufficient compaction between the particles, which reduces the filtration efficiency and increases the energy consumption; the insufficient formation of the filter cake will affect the control of the solid-liquid separation, and will cause more adsorbent to be entrained in the filtrate, affecting the purification effect.

[0153] Example 6 Adsorbent stability test:

[0154] Adsorbent regeneration: After the adsorption-desorption experiment, the filter cake formed by desorption is recovered, in which there are residues of carbon dioxide-based polyols. The viscosity of carbon dioxide-based polyols is relatively high. Dichloromethane is added to reduce its viscosity. The mass ratio of the filter cake and dichloromethane is 1:10-1:400. After centrifugation, solid and liquid are obtained. The solid is a combined modified activated carbon adsorbent. After the solid is dried under vacuum drying, the regeneration of the adsorbent is completed. The regenerated adsorbent can be used again for the adsorption and purification of carbon dioxide-based polyols. The adsorption performance is shown in Table 3.

[0155] Table 3 Adsorbent stability data table of examples and comparative examples

[0156]

[0157] Data analysis: According to Table 3, the adsorbent was desorbed and regenerated before the adsorption experiment was carried out. We can see from the data that for the combined modified activated carbon adsorbent, after two cycles of use, the adsorbent still showed good adsorption effects on phenolic compounds and cobalt and zinc ions, which shows that the combined modified activated carbon adsorbent has strong adsorption performance and high adsorbent stability. When the commercial coconut shell activated carbon used in Comparative Example 2 is used as an adsorbent for recycling, it can be inferred from the data that its adsorption effect gradually decreases and its adsorption capacity decreases. The combined modified activated carbon adsorbent used in the present invention can be separated in a low viscosity system and can be recycled and reused, greatly reducing costs.

[0158] In summary, it can be seen from the above embodiments and comparative examples that the present invention provides a method for removing phenolic compounds and metal ions from carbon dioxide-based polyols, which adopts a dynamic adsorption and pressure-swing desorption method, accurately controls low-frequency ultrasonic pre-adsorption, and dynamically monitors the adsorption equilibrium by heating mechanical stirring, and then passes through the step parameters of low-medium pressure pressure-swing desorption in an inert gas, and cooperates with the combined modified activated carbon adsorbent of the present invention. The above step parameters are related to each other, progressive layer by layer, and play an overall synergistic effect, so that the combined modified activated carbon adsorbent can quickly and effectively adsorb phenolic compounds and metal ions in carbon dioxide-based polyols, and the low-frequency ultrasonic pre-adsorption can accurately regulate the carbon dioxide The pore structure of carbon-based polyols, this regulation helps to optimize the adsorption performance, so that the combined modified activated carbon adsorbent can better adapt to the adsorption requirements of carbon dioxide-based polyols with greater viscosity; and the inert gas pressure-swing desorption process is more conducive to desorbing carbon dioxide-based polyols with greater viscosity from the combined modified activated carbon adsorbent, which can improve the desorption efficiency, and the pressure-swing desorption helps to desorb the substances adsorbed in the deep layer of the combined modified activated carbon adsorbent, not just the substances on the surface, and this deep desorption effect can improve the thoroughness of the overall desorption, improve the yield of purified carbon dioxide-based polyols, and also make the combined modified activated carbon adsorbent more fully utilized. The method of the present invention is simple and convenient to operate, and can make the removal rate of phenolic compounds in the purified carbon dioxide-based polyols as high as 99% or more, and the metal ion concentration is less than 10 ppm, and the carbon dioxide-based polyols with quality that meets the downstream production requirements can be obtained efficiently and quickly, with less metal residue, low chroma and high transparency. And the combined modified activated carbon adsorbent used in the present invention can be regenerated and recycled, and the adsorption effect of recycled use still maintains a high level, improving economic benefits.

[0159] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments can still be modified, or some of the technical features can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for removing phenolic compounds and metal ions from carbon dioxide-based polyols, characterized in that: It includes dynamic adsorption and pressure swing desorption steps, specifically including: (1) Dynamic adsorption: (1-1) adding a combined modified activated carbon adsorbent to a carbon dioxide-based polyol, wherein the combined modified activated carbon adsorbent accounts for 0.09-20 wt% of the mass of the carbon dioxide-based polyol, and pre-adsorbing the combined modified activated carbon adsorbent using low-frequency ultrasound, wherein the combined modified activated carbon adsorbent is a combination of nitrogen heterocycle-low-temperature plasma activation-carbon dioxide gas modification; (1-2) heating and mechanically stirring to achieve adsorption equilibrium, wherein the adsorption equilibrium refers to dynamic monitoring of the removal rate of phenolic compounds in the carbon dioxide-based polyol to reach more than 99%, and the dynamic monitoring refers to sampling and testing every 30 minutes; (2) Transformer solution: (2-1) transferring the adsorption equilibrium mixture into a pressurized filter tank, and filtering the mixture with an inert gas at a low pressure to form a filter cake, wherein the low pressure is 0.1-0.7 MPa; (2-2) then using an inert gas medium pressure rapid filtration, wherein the medium pressure is 1-3 MPa, and collecting the filtrate at the bottom of the pressure filtration tank to obtain the purified carbon dioxide-based polyol; The nitrogen heterocycle-low temperature plasma activation-carbon dioxide gas modification step specifically includes: the nitrogen heterocycle modification method is to add the nitrogen heterocycle modifier to the activated carbon dispersion according to the mass ratio of the nitrogen heterocycle modifier to the activated carbon of 1:0.5-20, and heat and reflux to prepare the nitrogen heterocycle modified activated carbon; The low-temperature plasma activation method comprises subjecting the nitrogen heterocyclic modified activated carbon to a low-temperature plasma surface treatment to obtain an activated adsorbent; the low-temperature plasma activation time is 10-60 min; and the low-temperature plasma activation gas is nitrogen; The carbon dioxide gas modification method is to prepare a solution of the activated adsorbent using water as a solvent, disperse and soak it, and purge it with a low-pressure carbon dioxide gas at a pressure of 0.2-1.5 MPa until the solution pH is 6-8, filter it, and vacuum dry it to obtain the combined modified activated carbon adsorbent; Wherein, the nitrogen heterocycle modified activated carbon is selected from any one or more of pyridine modified activated carbon, pyrrole modified activated carbon, pyrimidine modified activated carbon, benzimidazole modified activated carbon, and quinoline modified activated carbon.

2. The method according to claim 1, characterized in that: The combined modified activated carbon adsorbent further comprises a pre-dispersion step before combined modification, wherein the pre-dispersion refers to dispersing the activated carbon in deionized water to prepare an activated carbon dispersion to form an active and stable activated carbon precursor.

3. The method according to claim 1, characterized in that The specific surface area of ​​the combined modified activated carbon adsorbent is 3000-5000 m 2 / g, and the average volume particle size is 10-40 μm.

4. The method according to claim 1, characterized in that: In step (1-1), the low-frequency ultrasonic wave has a frequency of 20-40 kHz.

5. The method according to claim 1, characterized in that In step (1-2), the heating temperature is 30-90° C., the mechanical stirring time is 4-10 h, and the stirring rate is 800 r / min-1600 r / min.

6. The method according to claim 1, characterized in that The detection and calculation method of the removal rate of the phenolic compounds is as follows: using an ultraviolet spectrophotometer to detect the absorbance corresponding to the maximum absorption wavelength Amax of the phenolic compounds, and then calculating a standard curve according to the Lambert-Beer law, and finally obtaining the concentration of the phenolic compounds in the carbon dioxide-based polyol, and then calculating the removal rate of the phenolic compounds according to the following formula; ŋ represents the removal rate of phenolic compounds, C0 represents the initial concentration of phenolic compounds in the carbon dioxide-based polyol, in mg / L, C t It represents the concentration of phenolic compounds in CO2-based polyols after adsorption by the modified adsorbent, in mg / L.

7. The method according to claim 1, characterized in that The low-pressure filtration time is 0.5-2 h, and the temperature is 25±5°C.

8. The method according to claim 1, characterized in that The medium pressure rapid filtration time is 1-8 h, and the temperature is 20-90°C.

9. The method according to claim 1, characterized in that: The carbon dioxide-based polyol is prepared by polymerization reaction of carbon dioxide, propylene oxide and phenol initiator under the action of cobalt-zinc double metal cyanide catalyst, and has a viscosity greater than 7000 mPa·s at 70°C.

10. The method according to claim 1, characterized in that The contents of metal cobalt and zinc in the purified carbon dioxide-based polyol are both lower than 2 ppm, and the removal rate of phenolic compounds is above 99%.

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